1. Technical Field
The present invention relates to floor structures in which space below the floor is accessible, and more specifically to an accessible floor structure that is structurally integrated with the associated building structure.
2. Description of the Related Art
The increase in the use of computers, communication devices, and other electronic hardware has placed new demands on building designers. Users desire a large number of outlets for access to electrical power and communication signals, and they need the ability to change the location of such outlets on a regular, sometimes frequent basis. Power and data outlets have been located in, or under, a floor, typically in removable floor sections elevated above the original floor by supports. Two typical types of elevated floors are the pedestal floor and the low-profile floor.
The pedestal access floor has pedestals that consist of metal rods with a base plate at one end and a supporting plate on the other that supports removable horizontal panels, thus forming a raised floor structure. The metal rods are height adjustable and rest on a conventional solid floor deck. The solid floor deck may be made of wood, concrete, or a combination of metal deck and a concrete topping slab. The rods are arranged in a grid, typically square. The rods and plates support removable floor sections. The height of the rods is typically about 12 to 18 inches and can be adjusted to a desired height prior to installing the floor sections. Electrical power and data cables are laid between the solid floor deck and the underside of the floor sections. The cables penetrate the floor sections at a desired location to suit the user's needs. The penetrations may consist only of openings for cables, or may be junction boxes, similar to common electrical wall outlets. The penetrations may accommodate power wires, or signal cables such as cable television, speaker wire, computer networks, etc. In some designs, the space between the floor deck and the elevated floor sections is configured to enable the distribution of conditioned air through grilles and/or registers located in selected floor sections. A flooring system of the type described above is disclosed in U.S. Pat. No. 3,396,501, issued to D. L. Tate on Aug. 13, 1968.
There is a labor premium involved in having to locate and install the foregoing pedestal system. The pedestals must be braced to meet seismic code, further increasing labor and material costs. Moreover, the pedestals increase ceiling height requirements, and ultimately the height of the building, especially if the building has many stories, which increases the area of the exterior envelope, thereby increasing not only construction costs but also operating costs due to heat loss. If the pedestal access floor is only used in parts of a building, ramps or structural accommodations must be made for the changes in floor elevation. As users re-route electrical cables below the access floor, the pedestals may present an impediment in pulling cables to a new location. The access floor also represents another step in the construction schedule. The acoustical properties of this system are poor. The floor panels are usually relatively thin, and transmit sound both horizontally and vertically.
A second type of elevated floor is a low-profile design, which may be roughly 2½ inches to 4 inches high. This design does not use pedestals to raise and support the floor sections, but rather relies on “feet” at the corners of the sections to create the space above the solid floor deck and below the underside of the panel. The panels, with low “feet,” rest directly on the floor deck. This low-profile design is less costly than the pedestal floor, but still impacts the cost of a traditionally designed floor in a building because it requires the use of a solid floor deck. The problem of elevation changes between the existing conventional floor and accessible floor also remains. It may also increase the floor-to-floor height of a multi-story building, albeit less than a traditional pedestal floor.
There are also disadvantages to the low-profile floor compared to the pedestal floor. The space below the low-profile sections is not deep enough to be used to supply air. The resulting floor is not as stable, in either the horizontal or vertical dimension, as the pedestal access floor described above. Since the sections are not fastened to the floor deck, they can move when cable is being pulled and re-routed. In general, the smaller distance between the solid floor deck and the surface of the floor sections decreases the flexibility of the low-profile floor. Both types require an underlying solid floor deck for support, and to provide structural stability to the overall building structure.
In addition, the acoustical characteristics of both common types of elevated floors are typically very poor. They tend to transmit noise to a degree that makes them impractical for use in many environments.
Another type of accessible floor is disclosed in U.S. Pat. No. 3,583,121, issued to D. L. Tate on Jun. 8, 1971. This system includes two layers of bar joists laid one on top of the other at right angles thereto. Panels laid over the upper layer may be configured to be removable, to provide access to space underneath. One disadvantage of this system is the height of the two layers of joists and the added height this imparts to a building. Additionally, the joists must be laid at least as closely together as the width of the panels. The resulting weight and depth of the system is too great to be practical except where particularly heavy loads are imposed on the floor. Also, the joists have to be welded at each intersection greatly increasing field labor costs.